Air cleaning is necessary in the case that the air stagnancy occurs when the air conditioning device or the heating device is used in the room during the summer and winter periods, especially in large public places where people are gathering. In particular, since SARS spread through the world, people show more and more concerns about the air cleaning in the room. In order to clean the air in the room, not only should the fresh air be introduced into the room, but also should the bacteria, viruses, mildew and the like in the air be killed. Currently, a typical way of air cleaning includes a conventional air cleaner which produces negative ion by high voltage ionization. Some air conditioners have such kind of air cleaning unit. Besides, the ultraviolet sterilizing lamp used in hospitals can effectively kill the germina in the air. These two methods for air cleaning both have their respective advantages, but also have obvious disadvantages. For example, the negative oxyanion has a poor sterilizing effect, and the ultraviolet lamp can not be used for a long time and will hurt the human body when it irradiates on the body. Furthermore, conventional ventilation devices and air conditioning devices do not have air cleaning function, instead, they generally only have dust filtering devices. In addition, the cost for replacing the whole device is very high.